Method and system to increase heat input to a weld during a short-circuit arc welding process

ABSTRACT

A method and a system to increase heat input to a weld during an arc welding process. A series of electric arc pulses are generated between an advancing welding electrode and a metal workpiece using an electric arc welding system capable of generating an electric welding waveform to produce the electric arc pulses. A cycle of the electric welding waveform includes a pinch current phase providing an increasing pinch current level, a peak current phase providing a peak current level, a tail-out current phase providing a decreasing tail-out current level, and a background current phase providing a background current level. At least one heat-increasing current pulse of the cycle is generated, providing a heat-increasing current level, during the background current phase, where the heat-increasing current level is above the background current level. The cycle of the electric welding waveform with the at least one heat-increasing current pulse may be repeated until the arc welding process is completed.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

U.S. Pat. No. 4,972,064, issued on Nov. 20, 1990, is incorporated hereinby reference in its entirety. U.S. Pat. No. 6,051,810, issued on Apr.18, 2000, is incorporated herein by reference in its entirety. U.S. Pat.No. 6,498,321, issued on Dec. 24, 2002, is incorporated herein byreference in its entirety. U.S. patent application Ser. No. 11/861,379filed on Sep. 26, 2007 is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

Certain embodiments relate to electric arc welding. More particularly,certain embodiments relate to a method of increasing heat input to aweld during a gas metal arc welding (GMAW) short-circuit arc process.

BACKGROUND

Open root welding is used for pipe and single-sided plate welding insituations that preclude welding from both sides of the material. Thistype of welding is common in the petrochemical and process pipingindustries. For many years, pipe fabricators have been searching for afaster, easier method to make single-sided open root welds. It isdifficult, even for skilled welders, to weld open root pipe. Inflexiblepositioning makes pipeline welding more difficult, time consuming, andexpensive. Higher strength pipe steels are driving a requirement toachieve a low hydrogen weld metal deposit. Gas tungsten arc welding(GTAW) has been an available process capable of achieving the qualityrequirements, however, GTAW root welds are expensive to make. The gasmetal arc welding (GMAW) process has been avoided because of problemswith sidewall fusion and lack of penetration.

Conventional constant voltage (CV) GMAW welding processes produce a flatinternal bead, or “suck back” where the bead shrinks back into the rootdue to high weld puddle temperatures. GTAW welding produces good pipewelds, however, travel speeds may be slow and heat input may be high.Stick welding with cellulose electrodes provides good fusioncharacteristics but leaves deep wagon tracks (requiring more labor forgrinding), a very convex root weld, and a high hydrogen deposit.

The Surface Tension Transfer (STT) process has been developed to makesingle-sided root welds on pipe, for example. STT is a controlledshort-circuit transfer GMAW process that produces a low hydrogen welddeposit and makes it easier to achieve a high quality root weld in allpositions. STT eliminates the lack of penetration and poor sidewallfusion problems encountered when using the traditional short-arc GMAWprocess.

The STT process produces a low hydrogen weld metal deposit in open rootjoints with easier operation, better back beads, better sidewall fusion,and less spatter and fumes than other processes. STT differs from thetraditional GMAW short-arc welding process in that the arc current isprecisely controlled independently from the wire feed speed. Also, thearc current is carefully regulated to reduce puddle agitation and toeliminate violent “explosions” that occur during the traditionalshort-arc GMAW process.

Even though the current STT process is significantly better than thetraditional short-arc GMAW process, especially for root weldingapplication, the ability to better control heat input into the weld toachieve even better penetration without increasing the weld puddlefluidity is desired.

Further limitations and disadvantages of conventional, traditional, andproposed approaches will become apparent to one of skill in the art,through comparison of such approaches with embodiments of the presentinvention as set forth in the remainder of the present application withreference to the drawings.

BRIEF SUMMARY

A first embodiment of the present invention comprises a method ofincreasing heat input to a weld during an arc welding process bygenerating a series of electric arc pulses between an advancing weldingelectrode and a metal workpiece using an electric arc welding systemcapable of generating an electric welding waveform to produce theelectric arc pulses. The method includes:

(a) regulating an output current level of the waveform to a backgroundcurrent level to sustain an electric arc between the electrode and theworkpiece, producing a molten metal ball on a distal end of theelectrode;

(b) dropping the output current level below the background current levelin response to the molten metal ball shorting to the workpiece andextinguishing the electric arc, to allow the molten metal ball to wetinto a puddle on the workpiece;

(c) automatically increasing the output current level above thebackground current level to induce the molten metal ball to pinch offfrom the distal end of the electrode;

(d) decreasing the output current level below the background currentlevel as the molten metal ball pinches off from the distal end of theelectrode onto the workpiece, re-establishing an electric arc betweenthe electrode and the workpiece;

(e) increasing the output current level to a peak current level of thewaveform in response to re-establishing the electric arc;

(f) decreasing the output current level toward the background currentlevel, producing a next molten metal ball on the distal end of theelectrode;

(g) pulsing the output current level, between the background currentlevel and an intermediate current level being between the backgroundcurrent level and the peak current level, at a pre-defined pulse rateuntil a next short is established between the next molten metal ball andthe workpiece; and

(h) repeating steps (b) through (g) until the arc welding process iscompleted.

Another embodiment of the present invention comprises a method ofincreasing heat input to a weld during an arc welding process bygenerating a series of electric arc pulses between an advancing weldingelectrode and a metal workpiece using an electric arc welding systemcapable of generating an electric welding waveform to produce theelectric arc pulses. The method includes:

-   -   (a) generating a base cycle of the electric welding waveform        having a background current phase providing a background current        level, a peak current phase providing a peak current level, and        a tail-out current phase providing a monotonically decreasing        tail-out current level;    -   (b) generating a pinch current phase of the electric welding        waveform, between the background current phase and the peak        current phase, providing a monotonically increasing pinch        current level; and    -   (c) generating at least one heat-increasing current pulse of the        electric welding waveform, during the background current phase,        providing an intermediate current level being between the        background current level and the peak current level.

The method may further include periodically repeating the backgroundcurrent phase, the pinch current phase, the peak current phase, and thetail-out current phase in succession such that the background currentphase includes the at least one heat-increasing current pulse. Themethod may also include decreasing a current level of the electricwelding waveform below the background current level at an end of thebackground current phase, and decreasing a current level of the electricwelding waveform below the background current level at an end of thepinch current phase.

A further embodiment of the present invention comprises a system forincreasing heat input to a weld during an arc welding process bygenerating an electric welding waveform to produce a series of electricarc pulses between an advancing welding electrode and a metal workpiece.The system includes a first configuration of electronic components togenerate a background current phase, a peak current phase, and atail-out current phase of the electric welding waveform, wherein thebackground current phase provides a background current level, the peakcurrent phase provides a peak current level, and the tail-out currentphase provides a monotonically decreasing tail-out current level. Thesystem also includes a second configuration of electronic components togenerate a pinch current phase of the electric welding waveform, whereinthe pinch current phase provides a monotonically increasing pinchcurrent level. The system further includes a third configuration ofelectronic components to generate at least one heat-increasing currentpulse of the electric welding waveform during the background currentphase, wherein the at least one heat-increasing current pulse providesan intermediate current level that is between the background currentlevel and the peak current level. The system may further include afourth configuration of electronic components to decrease a currentlevel of the electric welding waveform below the background currentlevel at an end of the background current phase in response to theelectrode shorting to the workpiece. The system may also include a fifthconfiguration of electronic components to decrease a current level ofthe electric welding waveform below the background current level at anend of the pinch current phase in anticipation of the electrodede-shorting from the workpiece.

Another embodiment of the present invention comprises a system forincreasing heat input to a weld during an arc welding process bygenerating an electric welding waveform to produce a series of electricarc pulses between an advancing welding electrode and a metal workpiece.The system includes means for generating a background current phase, apeak current phase, and a tail-out current phase of the electric weldingwaveform, wherein the background current phase provides a backgroundcurrent level, the peak current phase provides a peak current level, andthe tail-out current phase provides a decreasing tail-out current level.The system further includes means for generating a pinch current phaseof the electric welding waveform, wherein the pinch current phaseprovides an increasing pinch current level. The system also includesmeans for generating at least one heat-increasing current pulse of theelectric welding waveform during the background current phase, whereinthe at least one heat-increasing current pulse provides an intermediatecurrent level that is between the background current level and the peakcurrent level. The system further includes means for periodicallyre-generating the background current phase, the pinch current phase, thepeak current phase, and the tail-out current phase in succession suchthat the background current phase includes the at least oneheat-increasing current pulse. The system may also include means fordecreasing a current level of the electric welding waveform below thebackground current level at an end of the background current phase inresponse to the electrode shorting to the workpiece. The system mayfurther include means for decreasing a current level of the electricwelding waveform below the background current level at an end of thepinch current phase in anticipation of the electrode de-shorting fromthe workpiece.

In accordance with an embodiment of the present invention, the arcwelding process may be a gas metal arc welding (GMAW) process using, forexample, argon and CO₂ as shielding gases, or CO₂ by itself. The weldingelectrode may include steel or stainless steel. In accordance with anembodiment of the present invention, the background current level may beabout 70 amps, the peak current level may be about 330 amps, and theintermediate current level may be about 210 amps. In accordance with anembodiment of the present invention, the pre-defined pulse rate of theheat-increasing current pulses may be about 333 Hz and a wire feed speedof the arc welding process may be about 150 inches per minute.

These and other features of the claimed invention, as well as details ofillustrated embodiments thereof, will be more fully understood from thefollowing description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates an exemplary embodiment of a cycle of an electricwelding waveform used in an arc welding process to increase heat inputto a weld;

FIG. 1B illustrates the various stages of the arc welding process overthe cycle of FIG. 1A using the electric welding waveform of FIG. 1A,showing the relationship between a welding electrode and a metalworkpiece;

FIG. 2 illustrates a functional block diagram of a first exemplaryembodiment of a system for generating the electric welding waveform ofFIG. 1;

FIGS. 3A-3D illustrate exemplary embodiments of portions of a modulatingwaveform as generated by the various capabilities of the system of FIG.2;

FIG. 4 illustrates a functional block diagram of a second exemplaryembodiment of a system for generating the electric welding waveform ofFIG. 1;

FIG. 5 illustrates a flowchart of a first exemplary embodiment of amethod of increasing heat input to a weld during an arc welding processusing the electric welding waveform of FIG. 1 and the system of FIG. 2or the system of FIG. 4;

FIGS. 6A-6B illustrate a flowchart and resulting electric weldingwaveform of a second exemplary embodiment of a method of increasing heatinput to a weld during an arc welding process using the system of FIG.4; and

FIG. 7 illustrates a flowchart of a third exemplary embodiment of amethod of increasing heat input to a weld during an arc welding processusing the electric welding waveform of FIG. 1 or the electric weldingwaveform of FIG. 6B and the system of FIG. 2 or the system of FIG. 4.

DETAILED DESCRIPTION

FIG. 1A illustrates an exemplary embodiment of a cycle 101 of anelectric welding waveform 100 used in an arc welding process to increaseheat input to a weld. FIG. 1B illustrates the various stages (A-E) ofthe arc welding process over the cycle 101 using the electric weldingwaveform of FIG. 1A, showing the relationship between a weldingelectrode 191 and a metal workpiece 199. During an arc welding process,a series of electric arc pulses are generated between the advancingelectrode 191 and the metal workpiece 199 using an electric arc weldingsystem capable of generating the electric welding waveform 100 toproduce the electric arc pulses. In general, the cycle 101 periodicallyrepeats during the arc welding process to produce the resultant weld.However, the cycle 101 may repeat without the same number of heatincreasing pulses 150 and possibly without a pinch current phase 120 ifa short condition does not occur.

The cycle 101 of the electric welding waveform 100 includes a backgroundcurrent phase 110 providing a background current level 111, a pinchcurrent phase 120 providing a monotonically increasing pinch currentlevel 121, a peak current phase 130 providing a peak current level 131,and a tail-out current phase 140 providing a monotonically decreasingtail-out current level 141.

During the background current phase 110, an electric arc 195 issustained between the electrode 191 and the workpiece 199 producing amolten metal ball 192 on a distal end of the electrode 191 (see stage Ain FIG. 1B). At stage B, the molten metal ball 192, still connected tothe electrode 191, shorts to the workpiece 199. When the short occurs,the arc 195 is extinguished and the current level of the waveform 100 isdropped below the background current level 111 to a current level 112,allowing the molten ball 192 to wet into a puddle on the workpiece 199.

During the pinch current phase 120, the current level of the waveform100 is increased monotonically (e.g., ramped upward) above thebackground current level 111, providing the increasing pinch currentlevel 121 which causes the shorted molten metal ball 192 to begin topinch off from the distal end of the electrode 191 into the puddle ofthe workpiece 199 as shown in stage C of FIG. 1B. As the molten metalball 192 is about to pinch off from the electrode 191, the current levelof the waveform 100 is again dropped below the background current level111 to a current level 112 to avoid spatter, and an arc 196 isre-established between the electrode 191 and the workpiece 199.

Once the arc 196 is re-established, the waveform 100 enters the peakcurrent phase 130. During the peak current phase 130, the current levelof the waveform 100 is increased to and held at the peak current level131. In accordance with an embodiment, the peak current level 131 is thehighest current level of the waveform 100 and establishes an arc 197between the electrode 191 and the workpiece 199 of sufficient strengthto begin forming a next molten metal ball 198 at the distal end of theelectrode 191.

After the peak current phase 130, the waveform 100 enters the tail-outcurrent phase 140. During the tail-out current phase 140, the currentlevel of the waveform 100 monotonically (e.g., exponentially) decreasestoward the background current level 111 providing the decreasingtail-out current level 141. The current of the waveform 100 inputs heatinto the weld. The tail-out current phase 140 acts as a coarse heatcontrol phase for the waveform 100 whereas the background current phase110 acts as a fine heat control phase for the waveform 100. However, incertain arc welding applications, it may be desirable to provideadditional heat input control.

After the tail-out current phase 140, the background current phase 110is again entered, providing the background current level 111 andproducing a substantially uniform next molten metal ball 198 at thedistal end of the electrode 191 (stage A). During the background currentphase 110, at least one heat-increasing current pulse 150 is generated,providing an intermediate current level 151 that is between thebackground current level 111 and the peak current level 131. The heatincreasing current pulse 150 may be periodically repeated within thebackground current phase 110 until a next short between the molten metalball 198 and the workpiece 199 occurs, at which time the arc 195 isextinguished and the current level of the waveform 100 is dropped belowthe background current level 111 to a current level 112, allowing thenext molten ball 198 to wet into the puddle on the workpiece 199 (stageB).

The heat-increasing current pulses 150 serve to re-heat the puddle andsurrounding area to increase penetration. Such an increase in heatprovided by the heat-increasing current pulses 150 may be desired in,for example, the welding of an open root joint in order to providebetter penetration without increasing the fluidity of the puddle. Theheat increasing pulses are not so large in amplitude as to transferdroplets across the arc and are not so wide in pulsewidth as to forcethe welding system above the short arc transition into globulartransfer. Again, in general, the cycle 101 periodically repeats duringthe arc welding process to produce the resultant weld. However, thecycle 101 may repeat without the same number of heat increasing pulses151 and possibly without the pinch current phase 120 if a short does notoccur. As used herein, the term “current level” refers to a currentamplitude which is substantially steady but may have some variations dueto the somewhat in-exact nature of producing an electric weldingwaveform.

As an example, in accordance with an embodiment of the presentinvention, the arc welding process is a gas metal arc welding (GMAW)process using argon and carbon dioxide as shielding gases. Thebackground current level 111 is about 70 amps, the peak current level131 is about 330 amps, and the intermediate current level 151 is about210 amps. The pulsewidth of a single heat-increasing pulse 150 is about1 millisecond and may be repeated about every 3 milliseconds, up tothree to six pulses during the background current phase 110. The periodof the cycle 101 is about 15 milliseconds.

FIG. 2 illustrates a functional block diagram of a first exemplaryembodiment of a system 200 for generating the electric welding waveform100 of FIG. 1. The system 200 provides power generation capability 210and modulating waveform generation and shaping capability 220 to createa modulating waveform 100′. The system 200 also provides short detectionand premonition detection (de-short anticipation) capability 230 todetect when a short condition occurs between the electrode 191 and theworkpiece 199 and to anticipate when a short condition is about toterminate (de-short condition) as a molten metal ball (e.g., 192)pinches off into the puddle on the workpiece 199.

A modulating waveform 100′ generated by the modulating waveformgeneration and shaping capability 220 is used to modulate the powergeneration capability 210 which provides electric current to theelectrode 191 and workpiece 199 in the form of the electric weldingwaveform 100. The modulating waveform generation and shaping capability220 includes a periodic base waveform generation capability 221. FIGS.3A-3D illustrate exemplary embodiments of portions of the modulatingwaveform 100′ as generated by the various capabilities of the system 200of FIG. 2. FIG. 3A illustrates a periodic base waveform portion 310generated by the periodic base waveform generation capability 221. Theperiodic base waveform generation capability 221 provides the generationof the background current phase 110, peak current phase 130, andtail-out current phase 140 of the modulating waveform 100′ in a periodicmanner.

The modulating waveform generation and shaping capability 220 alsoincludes a pinch current phase generation capability 222. FIG. 3Billustrates the periodic base waveform portion 310 of FIG. 3A having thepinch current phase 120 added. In accordance with an embodiment of thepresent invention, the pinch current phase 120 may be summed with theperiodic base waveform portion 310 using a signal summing capability 223of the modulating waveform generation and shaping capability 220.

The modulating waveform generation and shaping capability 220 furtherincludes a heat-increasing pulse generation capability 224. FIG. 3Cillustrates the periodic base waveform portion 310 of FIG. 3A having thepinch current phase 120 of FIG. 3B and having the heat-increasing pulses150 switched in during the background current phase 110. In accordancewith an embodiment of the present invention, the heat-increasing currentpulses 150 may be switched in during the background current phase 110using a signal switching capability 225 of the modulating waveformgeneration and shaping capability 220.

The modulating waveform generation and shaping capability 220 alsoincludes a sub-background current level generation (current reducing)capability 226. FIG. 3D illustrates the periodic base waveform portion310 of FIG. 3A having the pinch current phase 120 of FIG. 3B, thebackground current phase 110 having the heat-increasing current pulses150 as shown in FIG. 3C, and having the sub-background current portions112′ added. In accordance with an embodiment of the present invention,the sub-background current portions 112′ may be summed with the periodicbase waveform portion 310 and the pinch current phase 120 using thesignal summing capability 223 of the waveform generation and shapingcapability 220.

The resultant modulating waveform 100′ of FIG. 3D is used to modulatethe power generation capability 210 to provide the actual current levels(111, 112, 121, 131, 141, 151) of the various portions of the electricwelding waveform 100 to the electrode 191 and the workpiece 199 as shownin FIG. 1 and FIG. 2.

During a welding process using the system 200, the short detection andde-short anticipation capability 230 monitors current and voltage at theelectrode 191 and the workpiece 199 and detects when a short conditionoccurs between the electrode 191 and the workpiece 199 and alsoanticipates when the short condition is about to terminate (de-shortcondition). When a short condition occurs, the sub-background currentlevel capability 226 immediately pulls the current level of the waveform100 below the background current level 110 to a current level 112, inresponse to the short condition being detected, allowing a molten metalball to wet into a puddle on the workpiece 199 as described previouslyherein. Then the pinch current phase generation capability 222 appliesthe monotonically increasing pinch current level 121 to the waveform100.

When a de-short condition is anticipated (i.e., the molten metal ball isabout to pinch off from the distal end of the electrode), thesub-background current level capability 226 again pulls the currentlevel of the waveform 100 below the background current level 110 to thecurrent level 112, in response to the de-short condition beinganticipated, in order to avoid splatter. Furthermore, a timingcapability 227 of the waveform generation and shaping capability 220 istriggered. The timing capability 227 counts down over the time segmentsoccupied by the peak current phase 130 and the tail-out current phase140 until the waveform 100 reaches the background current phase 110.

In accordance with an embodiment of the present invention, the timingcapability is pre-programmed with the amount of time occurring betweenthe de-short condition and entrance into the background current phase110. Once the timing capability 227 finishes counting down, indicatingthat the background current phase 110 has been entered, the signalswitching capability 225 is triggered to switch in the heat-increasingpulses 150 from the heat-increasing pulse generation capability 224. Theheat-increasing pulses 150 are switched into the waveform 100 during thebackground current phase 110 until a next short condition is detected.

The various functional capabilities of the system 200 of FIG. 2 may beimplemented using configurations of electronic components which mayinclude analog and/or digital electronic components. Such configurationsof electronic components may include, for example, pulse generators,timers, counters, rectifiers, transistors, inverters, oscillators,switches, transformers, wave shapers, amplifiers, state machines,digital signal processors, microprocessors, and microcontrollers.Portions of such configurations may be programmable in order to provideflexibility in implementation. Various examples of such configurationsof electronic components may be found in U.S. Pat. Nos. 4,972,064,6,051,810, 6,498,321, and U.S. patent application Ser. No. 11/861,379,each of which is incorporated herein by reference in its entirety.

In accordance with an embodiment of the present invention, the system200 includes a first configuration of electronic components to generatethe background current phase 110, the peak current phase 130, and thetail-out current phase 140 of the electric welding waveform 100. Thesystem 200 further includes a second configuration of electroniccomponents to generate the pinch current phase 120 of the electricwelding waveform 100. The system 200 also includes a third configurationof electronic components to generate at least one heat-increasingcurrent pulse 150 of the electric welding waveform 100 during thebackground current phase 110.

In accordance with an embodiment of the present invention, the system200 also includes a fourth configuration of electronic components todecrease the current level of the electric welding waveform 100 belowthe background current level at an end of the background current phase110 in response to the electrode shorting to the workpiece. The system200 further includes a fifth configuration of electronic components todecrease the current level of the electric welding waveform 100 belowthe background current level at an end of the pinch current phase 120 inanticipation of the electrode de-shorting from the workpiece.

The first through fifth configurations of electronic components may notnecessarily be independent of each other but may share certainelectronic components. For example, in accordance with an embodiment ofthe present invention, many of the electronic components of the firstconfiguration may be the same as many of the electronic components ofthe third configuration. Similarly, many of the electronic components ofthe fourth configuration may be the same as many of the electroniccomponents of the fifth configuration. Other shared components may bepossible as well, in accordance with various embodiments of the presentinvention.

The functional implementation shown in FIG. 2 illustrates one exemplaryembodiment. Other embodiments are possible as well. For example, inaccordance with another embodiment, the pinch current phase 120 may beswitched into the modulating waveform 100′ via signal switchingcapability 225, instead of being summed in via signal summing capability223. Similarly, the heat-increasing pulses 150 may be summed into themodulating waveform 100′ via signal summing capability 223, instead ofbeing switched in via signal switching capability 225. In accordancewith another embodiment, the sub-background current level generationcapability 226 may not be present, or may be optional, allowinggeneration of a modulating waveform that does not include the currentlevel portions 112′. Other modified embodiments are possible as well,which result in generating the electric welding waveform 100 of FIG. 1or similar waveforms having at least one heat-increasing current pulseduring a background current phase.

FIG. 4 illustrates a functional block diagram of a second exemplaryembodiment of a system 400 for generating the electric welding waveform100 of FIG. 1. The system 400 is a state machine type of system as isdescribed herein. The Lincoln Electric Power Wave™ 450 system is anexample of a state machine type of welding system.

The system 400 includes a welding program 410 loaded onto a state basedfunction generator 420. In accordance with an embodiment of the presentinvention, the state based function generator 420 includes aprogrammable microprocessor device. The welding program 410 includes thesoftware instructions for generating an electric welding waveform. Thesystem further includes a digital signal processor (DSP) 430operationally interfacing to the state based function generator 420. Thesystem also includes a high speed amplifier inverter 440 operationallyinterfacing to the DSP 430.

The DSP 430 takes its instructions from the state based functiongenerator 420 and controls the high speed amplifier inverter 440. Thehigh speed amplifier inverter 440 transforms a high voltage input power441 into a low voltage welding output power in accordance with controlsignals 435 from the DSP 430. For example, in accordance with anembodiment of the present invention, the DSP 430 provides controlsignals 435 which determine a firing angle (timing of switch activation)for the high speed amplifier inverter 440 to produce various phases ofan electric welding waveform.

The outputs 442 and 443 of the high speed amplifier inverter 440 areoperationally connected to a welding electrode 450 and a workpiece 460respectively to provide a welding current which forms an electric arcbetween the electrode 450 and the workpiece 460. The system 400 alsoincludes voltage and current feedback capability 470 which senses avoltage between the electrode 450 and the workpiece 460 and which sensescurrent flowing through the welding circuit formed by the electrode 450,the workpiece 460, and high speed amplifier inverter 440. The sensedcurrent and voltage are used by the state based function generator 420to detect shorting of the electrode 450 to the workpiece 460 (i.e., ashort condition) and to detect when a molten metal ball is about topinch off from the electrode 450 (i.e., a de-short condition).

The system 400 further includes a current reducer 480 and a diode 490.The current reducer 480 and the diode 490 are operationally connectedbetween the outputs 442 and 443 of the high speed amplifier inverter440. The current reducer 480 also operationally interfaces to the DSP430. When a short condition occurs between the electrode 450 and theworkpiece 460, the DSP 430 commands the current reducer 480, via acontrol signal 436, to pull the current level through the weldingcircuit below a predefined background current level. Similarly, when ade-short condition occurs (i.e., a molten metal ball pinches off fromthe distal end of the electrode 450) the DSP 430 commands the currentreducer 480 to pull the current level through the welding circuit belowa predefined background current level. In accordance with an embodimentof the present invention, the current reducer 480 includes a Darlingtonswitch, a resistor, and a snubber.

FIG. 5 illustrates a flowchart of a first exemplary embodiment of amethod 500 of increasing heat input to a weld during an arc weldingprocess using the electric welding waveform 100 of FIG. 1 and the system200 of FIG. 2 or the system 400 of FIG. 4. In step 510, regulate anoutput current level of the waveform 100 to a background current level111 to sustain an electric arc 195 between an electrode (e.g., 191 or450) and a workpiece (e.g., 199 or 460), producing a molten metal ball192 on a distal end of the electrode (e.g., 191 or 450). In step 520,drop the output current level below the background current level 111 inresponse to the molten metal ball 192 shorting to the workpiece (e.g.,199 or 460) and extinguishing the electric arc 195, to allow the moltenmetal ball 192 to wet into a puddle on the workpiece (e.g., 199 or 460).In step 530, automatically increase the output current level above thebackground current level 111 to induce the molten metal ball 192 topinch off from the distal end of the electrode (e.g., 191 or 450).

In step 540, decrease the output current level below the backgroundcurrent level 111 as the molten metal ball 192 pinches off from thedistal end of the electrode (e.g., 191 or 450) onto the workpiece (e.g.,199 or 460), re-establishing an electric arc 196 between the electrode(e.g., 191 or 450) and the workpiece (e.g., 199 or 460). In step 550,increase the output current level to a peak current level 131 of thewaveform 100 in response to re-establishing an electric arc 196. In step560, decrease the output current level toward the background currentlevel 111, producing a next molten metal ball 198 on the distal end ofthe electrode (e.g., 191 or 450). In step 570, pulse the output currentlevel, between the background current level 111 and an intermediatecurrent level 151 being between the background current level 111 and thepeak current level 131, at a pre-defined pulse rate until a next shortis established between the next molten metal ball 198 and the workpiece(e.g., 199 or 460). In step 580, if the arc welding process is notcompleted, then proceed back to step 520, otherwise, end.

FIGS. 6A-6B illustrate a flowchart and resulting electric weldingwaveform 650 of a second exemplary embodiment of a method 600 ofincreasing heat input to a weld during an arc welding process using thesystem 400 of FIG. 4. In step 601, regulate an output current level ofan electric welding waveform 650 to a background current level 602. Whena short condition is detected, then in step 603, reduce the outputcurrent level to a sub-level 604 being below the background currentlevel 602 by triggering the current reducer 480. In step 605, startramping the output current level according to a pinch current ramp 606.When a de-short condition (pinch off) is detected, then in step 607,reduce the output current level again to a sub-level 604 by triggeringthe current reducer 480.

In step 608, regulate the output current level to a peak current level609 in response to re-establishing an arc between the electrode 450 andthe workpiece 460. In step 610, decrease the output current level fromthe peak current level 609 toward the background current level 602according to a monotonically decreasing tail-out current ramp 611. Instep 612, regulate the output current level to a heat increasing currentlevel 613 during a first pulse interval 614 forming a heat increasingcurrent pulse 615.

The method 600 may alternate between step 601 and step 612 (i.e., theoutput current may switch back and forth between the heat increasingcurrent level 613 and the background current level 602 formingsubsequent heat increasing current pulses) for a pre-determined numberof times, or until a next short condition is detected. Furthermore, inaccordance with an embodiment of the present invention, the pulse widthand amplitude of successive heat increasing current pulses 615′ may bethe same as or different from the pulse width and amplitude of the firstheat increasing current pulse 615, depending on the specifics of thewelding operation (e.g., weld metals, shielding gases, etc.).

FIG. 7 illustrates a flowchart of a third exemplary embodiment of amethod 700 of increasing heat input to a weld during an arc weldingprocess using the electric welding waveform 100 of FIG. 1 or theelectric welding waveform 650 of FIG. 6B and the system 200 of FIG. 2 orthe system 400 of FIG. 4. In step 710, generate a base cycle (e.g., 310)of an electric welding waveform (e.g., 100) having a background currentphase (e.g., 110) providing a background current level (e.g., 111), apeak current phase (e.g., 130) providing a peak current level (e.g.,131), and a tail-out current phase (e.g., 140) providing a decreasingtail-out current level (e.g., 141). In step 720, generate a pinchcurrent phase (e.g., 120) of the electric welding waveform (e.g., 100),between the background current phase (e.g., 110) and the peak currentphase (e.g., 130), providing an increasing pinch current level (e.g.,121). In step 730, generate at least one heat-increasing current pulse(e.g., 150) of the electric welding waveform (e.g., 100), during thebackground current phase (e.g., 110), providing an intermediate currentlevel (e.g., 151) being between the background current level (e.g., 111)and the peak current level (e.g., 131).

In summary, a method and a system to increase heat input to a weldduring an arc welding process is disclosed. A series of electric arcpulses are generated between an advancing welding electrode and a metalworkpiece using an electric arc welding system capable of generating anelectric welding waveform to produce the electric arc pulses. A cycle ofthe electric welding waveform includes a pinch current phase providingan increasing pinch current level, a peak current phase providing a peakcurrent level, a tail-out current phase providing a decreasing tail-outcurrent level, and a background current phase providing a backgroundcurrent level. At least one heat-increasing current pulse of the cycleis generated, providing a heat-increasing current level, during thebackground current phase, where the heat-increasing current level isabove the background current level. The cycle of the electric weldingwaveform with the at least one heat-increasing current pulse may berepeated until the arc welding process is completed. The heat-increasingcurrent pulses serve to re-heat the puddle and surrounding area toincrease penetration. Such an increase in heat provided by theheat-increasing current pulses may be desired in, for example, thewelding of an open root joint in order to provide better penetrationwithout increasing the fluidity of the puddle. The heat increasingpulses are not so large in amplitude as to transfer droplets across thearc and are not so wide in pulsewidth as to force the welding systemabove the short arc transition into globular transfer.

While the invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the invention without departing from its scope.Therefore, it is intended that the invention not be limited to theparticular embodiment disclosed, but that the invention will include allembodiments falling within the scope of the appended claims.

1. A method of increasing heat input to a weld during an arc weldingprocess by generating a series of electric arc pulses between anadvancing welding electrode and a metal workpiece using an electric arcwelding system capable of generating an electric welding waveform toproduce said electric arc pulses, said method comprising: (a) regulatingan output current level of said waveform to a background current levelto sustain an electric arc between said electrode and said workpiece,producing a molten metal ball on a distal end of said electrode; (b)decreasing said output current level below said background current levelin response to said molten metal ball shorting to said workpiece andextinguishing said electric arc, to allow said molten metal ball to wetinto a puddle on the workpiece; (c) automatically increasing said outputcurrent level above said background current level to induce said moltenmetal ball to pinch off from said distal end of said electrode; (d)decreasing said output current level below said background current levelas said molten metal ball pinches off from said distal end of saidelectrode onto said workpiece, re-establishing an electric arc betweensaid electrode and said workpiece; (e) increasing said output currentlevel to a peak current level of said waveform in response tore-establishing said electric arc; (f) decreasing said output currentlevel toward said background current level, producing a next moltenmetal ball on said distal end of said electrode; (g) pulsing said outputcurrent level, between said background current level and an intermediatecurrent level being between said background current level and said peakcurrent level, at a pre-defined pulse rate until a next short isestablished between said next molten metal ball and said workpiece; and(h) repeating steps (b) through (g) until said arc welding process iscompleted.
 2. The method of claim 1 wherein said arc welding process isa gas metal arc welding (GMAW) process.
 3. The method of claim 1 whereinsaid background current level is about 70 amps.
 4. The method of claim 1wherein said peak current level is about 330 amps.
 5. The method ofclaim 1 wherein said intermediate current level is about 210 amps. 6.The method of claim 1 wherein said pre-defined pulse rate is about 333Hz.
 7. The method of claim 2 wherein said GMAW process uses argon andCO.sub.2 as shielding gases.
 8. The method of claim 1 wherein a wirefeed speed of said arc welding process is about 150 inches per minute.9. A method of increasing heat input to a weld during an arc weldingprocess by generating a series of electric arc pulses between anadvancing welding electrode and a metal workpiece using an electric arcwelding system capable of generating an electric welding waveform toproduce said electric arc pulses, said method comprising: (a) generatinga base cycle of said electric welding waveform having a backgroundcurrent phase providing a background current level, a peak current phaseproviding a peak current level, and a tail-out current phase providing adecreasing tail-out current level; (b) generating a pinch current phaseof said electric welding waveform, between said background current phaseand said peak current phase, providing an increasing pinch currentlevel; and (c) generating at least one heat-increasing current pulse ofsaid electric welding waveform, during said background current phase,providing a heat-increasing current level that is between saidbackground current level and said peak current level.
 10. The method ofclaim 9 further comprising periodically repeating said backgroundcurrent phase, said pinch current phase, said peak current phase, andsaid tail-out current phase in succession such that said backgroundcurrent phase includes said at least one heat-increasing current pulse.11. The method of claim 9 further comprising decreasing a current levelof said electric welding waveform below said background current level atan end of said background current phase.
 12. The method of claim 10further comprising decreasing a current level of said electric weldingwaveform below said background current level at an end of said pinchcurrent phase.
 13. The method of claim 9 wherein said arc weldingprocess is a gas metal arc welding (GMAW) process using argon andCO.sub.2 as shielding gases.
 14. The method of claim 9 wherein saidbackground current level is about 70 amps.
 15. The method of claim 9wherein said peak current level is about 330 amps.
 16. The method ofclaim 9 wherein said heat-increasing current level is about 210 amps.17. The method of claim 9 wherein a wire feed speed of said arc weldingprocess is about 150 inches per minute.
 18. A system for increasing heatinput to a weld during an arc welding process by generating an electricwelding waveform to produce a series of electric arc pulses between anadvancing welding electrode and a metal workpiece, said systemcomprising: a welding power source configured to generate a backgroundcurrent phase, a peak current phase, and a tail-out current phase ofsaid electric welding waveform, wherein said background current phaseprovides a background current level, said peak current phase provides apeak current level, and said tail-out current phase provides amonotonically decreasing tail-out current level; said welding powersource further configured to generate a pinch current phase of saidelectric welding waveform, wherein said pinch current phase provides amonotonically increasing pinch current level; and said welding powersource is further configured to generate at least one heat-increasingcurrent pulse of said electric welding waveform during said backgroundcurrent phase, wherein said at least one heat-increasing current pulseprovides an intermediate current level that is between said backgroundcurrent level and said peak current level.
 19. The system of claim 18,wherein said welding power source is further configured to decrease acurrent level of said electric welding waveform below said backgroundcurrent level at an end of said background current phase in response tosaid electrode shorting to said workpiece.
 20. The system of claim 19,wherein said welding power source is further configured to decrease acurrent level of said electric welding waveform below said backgroundcurrent level at an end of said pinch current phase in anticipation ofsaid electrode de-shorting from said workpiece.
 21. A system forincreasing heat input to a weld during an arc welding process bygenerating an electric welding waveform to produce a series of electricarc pulses between an advancing welding electrode and a metal workpiece,said system comprising: means for generating a background current phase,a peak current phase, and a tail-out current phase of said electricwelding waveform, wherein said background current phase provides abackground current level, said peak current phase provides a peakcurrent level, and said tail-out current phase provides a decreasingtail-out current level; means for generating a pinch current phase ofsaid electric welding waveform, wherein said pinch current phaseprovides an increasing pinch current level; and means for generating atleast one heat-increasing current pulse of said electric weldingwaveform during said background current phase, wherein said at least oneheat-increasing current pulse provides an intermediate current levelthat is between said background current level and said peak currentlevel; and means for periodically re-generating said background currentphase, said pinch current phase, said peak current phase, and saidtail-out current phase in succession such that said background currentphase includes said at least one heat-increasing current pulse.
 22. Thesystem of claim 21 further comprising means for decreasing a currentlevel of said electric welding waveform below said background currentlevel at an end of said background current phase in response to saidelectrode shorting to said workpiece.
 23. The system of claim 22 furthercomprising means for decreasing a current level of said electric weldingwaveform below said background current level at an end of said pinchcurrent phase in anticipation of said electrode de-shorting from saidworkpiece.